I wanted to suggest The Wurzels - Combine Harvester. It's not a gorey kill-them-all kind of song, but it can take on a twist of sick sadistic happy killings. Plus the lyrics are about farm places - and TF2 seems to have a tonne of farm paraphernalia.

Originally Posted by The Immortal Black MageThe sacrament of Dakka can be expressed only by those who have experienced it. It is a holy sacrament (of fire) that states "We are firing our guns at you. Die."